The present invention relates to the field of metal honeycomb catalyst supports, and especially those catalyst supports which are used in automobiles.
One way to make a metal honeycomb catalyst support is to lay a corrugated strip of metal on a flat strip of metal, and to wind the two strips upon themselves to make a spiral. Spiral-wound catalyst supports have a fatal shortcoming when they are used in catalytic converters for automobiles: they telescope outwardly under the pulsating flow of the engine exhaust. A method that has been used to prevent the telescoping consists of brazing together the layers of the spiral over a short length of spiral, at both ends of the spiral. This method is expensive, and moreover, it restricts the metal alloy of the spiral to metals that can be brazed. Such alloys do not always make satisfactory catalyst supports.
Another way to make a honeycomb is to fold a strip of metal back and forth upon itself. My U.S. Pat. No. 4,576,800, the disclosure of which is incorporated by reference herein, describes such a honey-comb. A plurality of slots are punched in the metal strip, at predetermined intervals. The slots define lines across the width of the strip, and the strip is folded along these lines. If the intervals between the lines of slots are calculated correctly, the face of the honeycomb will have the desired shape, such as a circle or an ellipse, which is commonly used for automobile converters. When the strip is folded, the slots form notches. The notches together define grooves which mate with ridges in the canister, thereby preventing the layers of the honeycomb from telescoping.
The catalytic converter described above has disadvantages due to the need to punch slots in the metal strip. The metal strips used in catalytic converters are typically very thin, of the order of 0.0015-0.003 inches. When the strip is this thin, the tolerance on the punch and die that forms the slots is measured in tenths of thousandths of an inch. Only a small amount of wear makes the punch and die inoperative.
The present invention provides an improved structure for a catalytic converter for an automobile. The invention provides a converter made of a folded metal strip which is firmly anchored within its canister, and having layers which cannot telescope outwardly. The invention is adapted to economical, high-speed mass production, and eliminates the need for a punch and die.